Impact of brewer's spent grain (BSG) and bio-transformed BSG biscuits on metabolic and gut health in adults with metabolic impairments: a randomized controlled trial.

BACKGROUND

Brewers’ spent grain (BSG), a fiber-rich by-product of the brewing industry, has high nutritional value. Fermentation with Rhizopus oligosporus further enhances its composition by increasing soluble dietary fiber and releasing antioxidants, potentially conferring superior metabolic regulatory and prebiotic effects. This study evaluated the effect of long-term consumption of BSG or fermented BSG-containing biscuits on metabolic and gut health in Singapore adults with metabolic impairments.

METHODS

Thirty-one metabolically impaired subjects were randomized to consume 90 g/day of control biscuits (Control, n = 11), 30% wheat flour substituted autoclaved BSG- (ABSG, n = 10) or fermented BSG-containing biscuits (FBSG, n = 10) for 12 weeks. Anthropometric, blood pressure, dietary intake, glycemic-related biomarkers, lipid-lipoprotein profile, gut microbiome and metabolites were assessed at baseline and after intervention.

RESULTS

Total dietary fiber intake increased in both ABSG and FBSG groups (Pinteraction < 0.001). FBSG group showed significant increase of HDL-C after intervention (P = 0.024). BSG-containing biscuits consumption decreased fecal lithocholic acid concentration (Pinteraction = 0.02), which may lower intestinal cytotoxicity. Although α- and β-diversity were unchanged, favorable taxonomic shifts were observed. In the ABSG group, Romboutsia, a genus associated with metabolic dysfunction, decreased while the FBSG group showed increased abundances of the short-chain fatty acids-producing Roseburia and Clostridium scindens, alongside a reduction in Dorea. asa No significant difference was observed in other indicators.

CONCLUSIONS

Consumption of BSG-containing biscuits enhances daily dietary fiber intake and modulates gut metabolites and microbiome composition to support gut microbiome homeostasis. Additionally, fermented BSG provides further metabolic benefits, particularly in regulating lipid-lipoprotein metabolism. TRIAL REGISTRATION: ClinicalTrials.gov: NCT05529108.